Our purpose is the study of the nature and regulation of the steps and events during mitochondrial biogenesis in yeast. We are interested in the nature and composition of the polypeptide products encoded in mitochondrial DNA and in their interaction with those mitochondrial polypeptides which have to be imported into the organelle for the construction of its functional inner membrane. To this end we are investigating a number of mutants, in both nuclear and mitochondrial DNA, with defined lesions in the products of mitochondrial protein synthesis. Some of these mutants as well as other approaches will be used to probe problems of integration and reciprocal regulation between the mitochondrial and nucleocytoplasmic compartments of the cell.